Cyclic unsaturated aldehydes are compounds which are useful as the raw materials of traction oils and unsaturated polyester resins, modifiers for phenolic resins, and functional chemical products such as monomers for functional resins.
On the other hand, a fluid for traction drive is used in a traction drive device (a friction drive device by rolling contact), for example, a continuously variable transmission for a car or a continuously variable transmission for an industry, and such a fluid requires a high traction coefficient, stability to heat and oxidation, and economy. economy.
Known examples of the fluid for the traction drive include hydrocarbon compounds having a norbornane skeleton such as 2-formyl-methylbicyclo2,2,1!hepta-5-ene and 2-formyl-dimethylbicyclo2,2,1!hepta-5-ene in which cyclic unsaturated aldehydes are intermediates for synthesis (Japanese Patent Application Laid-open No. 95295/1991), and hydrocarbon compounds having a bicyclooctane skeleton such as 2-formyl-methylbicyclo2,2,2!octa-5-ene and 2-formyl-dimethylbicyclo2,2,2!octa-5-ene in which cyclic unsaturated aldehydes are intermediates for synthesis (Japanese Patent Application Laid-open No. 9134/1993).
The above-mentioned 2-formyl-methylbicyclo2,2,2!-hepta-5-ene or 2-formyl-dimethylbicyclo2,2,2!hepta-5-ene can generally be obtained by reacting cyclopentadiene or methylcyclopentadiene with crotonaldehyde in accordance with the Diels-Alder reaction, and the above-mentioned 2-formyl-methylbicyclo 2,2,2!octa-5-ene or 2-formyl-dimethylbicyclo-2,2,2!octa-5-ene can generally be obtained by reacting 1,3-cyclohexadiene or methyl-1,3-cyclohexadiene with crotonaldehyde in accordance with the Diels-Alder reaction. If no catalyst is used in such a Diels-Alder reaction, a high temperature of 100.degree. C. or more is required, because crotonaldehyde is less reactive. As a result, polymers of the cyclic conjugated diene compound and crotonaldehyde which are the starting materials are formed, or heavy compounds are formed by the further addition of the diene compound to the desired product, so that a yield of the desired product deteriorates inconveniently. As the catalysts for the Diels-Alder reaction, for example, Lewis acids such as titanium tetrachloride and ethylaluminum dichloride are heretofore known, but since they are liquid, a post-treatment is necessary after the reaction, and they are liable to corrode an apparatus. Therefore, they are not suitable for industrial production. In consequence, it has been demanded to develop a catalyst which does not require the post-treatment and which has no corrosive properties.
With regard to the Diels-Alder reaction of crotonaldehyde and cyclopentadiene, there has been reported an embodiment in which the reaction is carried out at 100.degree. C. for 4 hours without using any catalyst "Ann.", Vol. 470, p. 62, (1929)!. However, the above conditions lead to the formation of large amounts of by-products such as a polymer of the cyclopentadiene and crotonaldehyde, and a condensate in which 2 mol of cyclopentadiene is added to crotonaldehyde, with the result that the selectivity of the desired product is low.
On the other hand, as reaction embodiments using the catalyst, there have been reported an embodiment in which the reaction is carried out at -78.degree. C. for 1.5 hours in the presence of a catechol boron bromide catalyst (yield=70%), an embodiment in which the reaction is carried out at -78.degree. C. for 1 hour by the use of a ferrocenium hexafluorophosphate catalyst (yield=78%) "Tetrahedron Letters", Vol. 30, p. 1357 (1989)!, and an embodiment in which the reaction is carried out at -78.degree. C. for 1 hour in the presence of a 2-chloro-1,3,2-dithiaborane catalyst (yield=72%) "Tetrahedron Letters", Vol. 34, p. 4095 (1993)!. In these methods, however, the homogeneous reaction is done at a low temperature in the presence of the expensive catalyst by the use of the solvent, and hence they cannot industrially be applied at all.
With regard to the Diels-Alder reaction using a heterogeneous solid catalyst, there are known an embodiment in which cyclopentadiene is reacted with acrolein, acrylic acid or acrylonitrile in the presence of silica, alumina or a cellulose catalyst "Angew. Chem.", Vol. 93, p. 1114 (1981)!, an embodiment in which cyclopentadiene is reacted with crotonic acid in the presence of a silica catalyst or an alumina catalyst "Anorg. Chem.", Org. Chem., Vol. 36B, p. 898 (1981)!, an embodiment in which safflower oil is reacted with maleic anhydride in the presence of a silica-alumina catalyst "Oil Chemistry", Vol. 27, p. 435 (1978)!, and an embodiment in which methylcyclopentadiene is reacted with maleic anhydride in the presence of a catalyst such as silica-alumina, silica-magnesia, alumina-boria, active terra abla, solid phosphoric acid or a cation exchange resin (Japanese Patent Application Laid-open No. 73043/1994). However, a specific technique is not known so far in which the cyclic conjugated diene compound is reacted with an aldehyde having a lower alkyl group at the third position of an acrolein such as crotonaldehyde in the presence of a solid acid catalyst in accordance with the Diels-Alder reaction.